1. Field of the Invention
The present invention relates to a food container suitable for cooking through use of a microwave oven.
2. Description of the Related Art
Japanese Patent Application Laid-Open No. 6-329179 discloses a food container suitable for cooking through use of a microwave oven. As shown in FIGS. 1A-1C, the food container has a small hole 1, and a circular cover film 2 is attached to the container via an adhesive layer 3 in order to cover the hole 1. In the adhesive layer 3 is formed a triangular non-adhesive area 4. In this way, the small hole 1, the cover film 2, and the adhesive layer 3 constitute a pressure regulation valve 5.
When the food container containing food therein is cocked in a microwave oven, the food is heated so that moisture is produced from the food. Until the vapor pressure within the food container reaches a predetermined level, the pressure regulation valve 5 remains closed. When the vapor pressure within the food container reaches the predetermined level, as shown in FIG. ID, the sheet 2 partially separates from the food container in order to relieve the vapor pressure. Thus, the food is cooked in a desirable manner. Also, the package container is prevented from bursting due to the vapor pressure.
However, in the conventional food container, the inner circumferential surface 3a of the adhesive layer 3 is exposed to the atmosphere within the container containing a large amount of moisture. Therefore, during long-time storage, the adhesive force of the adhesive layer 3 may be deteriorated, resulting in improper operation of the pressure regulation valve. Further, chemicals contained in the adhesive layer 3 may dissolve and enter the interior of the container, possibly imparting an odor to the food.
In addition, if food contained in the food container produces liquid during cooking, the liquid may spout through the hole and dirty the interior of a microwave oven.